The present invention relates to an optical element capable of simultaneously outputting sound from the surface of a display device with an image, the optical element comprising: a first electrode member; a first dielectric elastomer layer disposed on the first electrode member; a second electrode member disposed on the first dielectric elastomer layer; and an optical crystal layer disposed on the second electrode member. Accordingly, in the present invention, image and sound are implemented simultaneously, and thus, it is possible to prevent defects due to mismatching of the image and the sound, and a separate sound system is not required when the display device is manufactured using the optical element, thereby making it possible to reduce components of an electronic product including the display device and reduce the manufacturing cost.